Ep additive for mixed lithium-calcium base greases



United States Patent 6 EP ADDITIVE FOR MIXED LITHIUM-CALCIUM BASE GREASES James R. Roach, Beacon, and John P. Dilworth, Fishkill, N.Y., assigns to The Texas Company, New York, N.Y., a corporation of Delaware N Drawing. Application October 27, 1954 Serial No. 465,126

5 Claims. (Cl. 252-40) This invention relates to a mixture of additives which 7 possess a synergistic EP action in mixed lithium-calcium 5: 1. The trihydrocarbon phosphite component of this mixture has the general formula I OH ROP/ wherein R, R and R" are alkyl, alkenyl, cycloaliphatic, aryl, alkaryl, or aralkyl radicals which may be the same or different. The dihydrocarbon selenide has a general formula R-SeR wherein the scopes of R and R are identical with that of the R components of the trihydrocarbon phosphite. The hydrocarbon group in either the phosphite or the selenide contains 1 to 30 carbon atoms. A hydrocarbon chain length of 3 to carbon atoms is preferred in the phosphite component and a chain length of 8 to 18 carbon atoms is preferred in the selenide component.

The synergistic EP action of the phosphite ester-hydrocarbon selenide combination is limited to greases containing a mixture of lithium-calcium soaps as the thickening agent. In greases containing either a lithium or a calcium soap as the sole thickening agent, better EP properties are obtained with the phosphite ester alone than with a mixture of phosphite ester and selenide.

The greases whose EP properties are improved by the two-component additive of this invention comprise 5 to 25 weight percent mixed lithium and calcium soaps, an oleaginous lubricating base as the major component, 2 to 5 percent phosphite ester and 0.5 to 2.5 percent selenide. Other additives can be incorporated to impart other desirable properties such as anticorrosive properties and anti oxidant properties to the grease; diphenylamine and phenyl-alpha-naphthylamine which act as antioxidants are examples of such additives.

Phosphite esters have been widely used as anti-corrosive agents and antioxidants in lubricants particularly in lubricating oils and are known to possess some extreme pressure properties. A large number of trihydrocarbonsubstituted phosphite esters are commercially available and sold as lube oil additives. Among these may be mentioned triamyl phosphite, tricyclohexyl phosphite, triphenyl phosphite and tritolyl phosphite. In addition to ICC these commercially available phosphites other phosphite esters corresponding to the general formula wherein R, R and R" designate hydrocarbon radicals such as alkyl, alkenyl, aryl, cycloaliphatic, alkaryl and aralkyl, are used in the synergistic combination of this invention. Additional useable phosphite esters are tribenzyl phosphite, triethyl phosphite, tri-2-propenyl phosphite, tri-2-ethylhexyl phosphite, tri-Z-methylcyclohexyl phosphite, and tridecyl phosphite. The preferred chain length of the hydrocarbon radical is 3 to 10 carbon atoms.

Dihydrocarbon selenides have also been used as lubricant additives. Selenides are known as antioxidants but do not possess extreme pressure properties when used per se. As a matter of fact, the incorporation of selenides per se in greases tends to depress their extreme pressure properties. In the general formula R-Se-R, R and R are alkyl, alkenyl, aryl, alkaryl, aralkyl or cycloaliphatic radicals. Dialiphatic selenides are preferred for use in the synergistic EP additive of the invention. The preferred chain length of the hydrocarbon radical is 8 to 18 carbon atoms in both acyclic and cyclic selenides. Representative selenides are the following: dilauryl selenide, di-2-ethylhexyl selenide, diamyl selenide, ditetradecyl selenide, dioctadecyl selenide, di-2-decenyl selenide, di-S- hexenyl selenide, diphenyl selenide, dixylyl selenide, diethylcyclohexyl selenide, dibenzyl selenide and di-4-tertiary butyl phenyl selenide. Particularly preferred selenides for use in the formulation of the EP additive mixture are dilauryl selenide, di-Z-ethylhexyl selenide, and di-tetradecyl selenide.

Preferred phosphite-selenide combinaitons are triamyl phosphite-dilauryl selenide, triamyl phosphite-di-Z-ethylhexyl selenide, triamyl phosphite di-tetradecyl selenide, tri- 2-ethylhexy1 phosphite-dilauryl selenide, triphenyl phosphite-dilauryl selenide and triphenyl phosphite-di-Z-ethylhexyl selenide.

The additive comprises phosphite and selenide in a Weight ratio of 1:1.25 to 10:1. The most widely used additive combinations generally comprise phosphite and selenide in a weight ratio between 2:1 to 5: 1. A particularly effective mixture comprises 3 parts triamyl phosphite and 1 part of dilauryl selenide.

Conventional soap-forming materials may be employed in the production of the lithium-calcium soap component of the grease of this invention. Examples of such conventional soap-forming materials are stearic acid, tallow, lard oil, etc., which contain saturated or unsaturated high molecular weight fatty acids. The preferred soap-forming material for use in the production of the extreme pressure grease of this invention comprises at least a major portion of a hydroxy fatty acid, and contains at least 12 to 24 hydrocarbons. The hydroxy fatty acid can be used per se or in the form of an ester such as a glyceride or a monoalkyl ester. The most widely used hydroxy fatty acid is 12-hydroxy stearic acid but other hydroxy fatty acids such as 9-hydroxy stearic acid, IO-hydroxy stearic acid, 8-hydroxy palmitic acid, 7-hydroxy tetradecanoic acid and 9,10-dihydroxy. stearic acid may be used. Preferred acidic components comprise at least of the mixed lithium-calcium soap, they may be blended or combined with the conventional saturated fatty acids or fats in such proportions that at least 50 percent of the total acidic component is comprised of the hydroxy fatty acids or esters thereof. These fats and fatty acids include mixtures of fatty acid glycerides found in naturally occurring fats and oils, together with fractionated components thereof. The fatty acids may be a mixture of acids split off from these fats or prepared from hydrogenation of fish oils, or the individual acids themselves. Very satisfactory results are secured by employing as the fatty material for the formation of the lithium-calcium soap a mixture of about 60-80 percent of hydrogenated castor oil or 12-hydroxy stearic acid with 40-20 percent of a saturated fatty acid such as stearic acid.

Although the synergistic action of phosphite-selenidc mixture is effected in lithium-calcium base greases containing 10 to 90 parts lithium soap to 90-10 parts calcium soap, it is particularly effective in the lithiumcalcium base greases in which the soap thickening agent contains 30 to 70 parts lithium metal and 70 to 30 parts calcium metal. The preferred grease obtained using the synergistic EP combination of this invention comprises 6 to 25 percent of a soap, in which the metal comprises 70 to 30 parts lithium and 30 to 70 parts calcium and in which the acidic component comprises at least 50 percent of a hydroxy fatty acid, an oleaginous lubricating base, 2.0 to weight percent phosphite ester and 0.5 to 2.5 weight percent selenide. Greases of this composition possess outstanding low-temperature torque properties and are characterized by superior extreme pressure properties.

The liquid lubricating base of the lithium-calciinn grease composition of the invention preferably comprises a major proportion of a synthetic oleaginous lubricating compound or condensation product, many types of which are now known in the art. Very satisfactory synthetic lubricants of this character are represented by the high molecular weight high boiling liquid aliphatic dicarboxylic acid esters which are Within the lubricating oil viscosity range and which possess lubricating properties. Compounds within this particular class are the esters of such acids as sebacic, adipic, pimelic, azelaic, alkenylsuccinic, alkylmaleic, etc. The esters thereof are preferably the aliphatic esters and particularly the branched chain aliphatic diesters. Specific examples of the preferred oleaginous compounds are di-Z-ethylhexyl sebacate, di-Z-ethylhexyl azelate, di-Z-ethylhexyl adipate, disec-amyl sebacate, di-Z-ethylhexyl alkenylsuccinate, di- Z-ethoxyethyl sebacate, di-2-(2-methoxyethoxy) ethyl sebacate, di-2-(2'-ethylbutoxy) ethylsebacate, di-2-butoxyethyl azelate, di-2-(2-butoxyethoxy) ethyl alkenylsuccinate, etc.

In addition to the aliphatic dicarboxylic acid esters described above, polyester lubricants fornied by a reaction of an aliphatic dicarboxylic acid, a glycol and a monofunctional compound, which is either an aliphatic monohydroxy alcohol or an aliphatic monocarboxylic acid, in specified mol ratios are also employed as the synthetic lubricating base in the compositions of this in vention; polyesters of this type are described in US. 2,628,974. Polyesters formed by reaction of a mixture containing specified amounts of 2-ethyl-1,3-hexanediol, sebacic acid and 2-ethylhexanol and by reaction of a mixture containing adipic acid, diethylene glycol and Z-ethylhexanoic acid illustrate this class of synthetic polyester lubricating bases.

Water-insoluble polyalkylene ethers as illustrated by polyglycols are also used as a synthetic lubricating base in the compositions of this invention. Polypropylene glycol, polybutylene glycols and mixed polyethylene-polypropylene glycols are examples of this class of synthetic lubricating bases.

The sulfur analogs of the above-described diesters, polyesters and polyalkylene ethers are also used in the formulation of the lubricating compositions of this invention. Dithioesters are exemplified by di-Z-ethylhexyl thiosebacate and di-n-octyl thioadipate; polyethylene thioglycol is an example of the sulfur analogs of the polyalkylene glycols; sulfur analogs of polyesters are exemplified by the reaction product of adipic acid, thioglycol and Z-ethylhexyl mercaptan.

Tetra-hydrocarbon-substituted silicates having a general formula 0R!!! RO-S iOR wherein R, R, R and R' are similar or dissimilar hydrocarbon radicals may also be used as a part of the oleaginous lubricating base. Tetra-aliphatic esters such as tetra-octyl silicate, tetra-lauryl silicate, tetra-amyl silicate and tetra-decyl silicate are preferred silicate esters but aryl esters such as tetra-phenyl silicate and cycloaliphatic silicates such as tetra-cyclohexyl silicates may also be used.

These oleaginous compounds may be used as the sole oil component of the grease or they may be blended with a mineral lubricating oil. Where a blend is employed, and low temperature properties are required, the mineral lubricating oil is preferably a light refined distillate mineral lubricating oil, such as a naphthene or parafiin base distillate, having an SUS viscosity at 100 F. of about 50 to 130 and preferably about 100. The mineral lubricating oil will generally constitute less than 50 percent of the blend, and ordinarily about 40-20 percent thereof.

The mineral lubricating oil is advantageously used where the lithium-calcium soap is formed in situ. In such case, the saponification of the fatty material with the mixture of lithium hydroxide and calcium hydroxide and dehydration of the resulting soap are conveniently carried out in the presence of a portion of the mineral lubricating EXAMPLE I An anhydrous calcium l2-hydroxy stearate grease was prepared by the procedure described in the copending application Serial No. 388,426, filed October 26, 1953, in the names of I. P. Dilworth, C. H. Culnane and R. F. Nelson, now abandoned. This grease comprised 11.7 Weight percent calcium l2-hydroxy stearate, 0.2 percent excess lime, 84.6 percent base oil, 3.0 percent of sorbitan monooleate and 0.5 percent of a mixture of parts diphenylamine and 5 parts salicylal amino guanidine oleate. This grease had a mean Hertz load of 22 kg. The

eifect of adding a phosphite, a selenide and a phosphiteselenide combination to this grease, identified as Ca base grease, is shown in Table I.

Table I Mean Composition Hertz Load, kg.

" 0a Base Grsasi 22 Ca Base Grease +1% dllauryl selenide 20 Ca Base Grease +3% triamyl phosphite 34 0a Base Grease +1% dilauryl selenide and 3% triamyl phosphite 2B The data in Table I demonstrate that dilauryl selenide per se suppresses the extreme pressure properties of the anhydrous calcium base grease and that the diamyl phosphite itself gives substantially better extreme pressure properties than the phosphite-selenide mixture. These data prove that a phosphite-selenide mixture has no synergistic EP action in an anhydrous calcium base grease.

EXAMPLE II There was prepared an anhydrous calcium grease stabilized with 1.1 weight percent of glycerol monostearate and 2.0 weight percent wool grease, and having the following approximate composition: 12.0 weight percent calcium soap of hydrogenated fish oil fatty acids, 84.3 weight percent parafiin base oil, 1.2 weight percent glycerol monostearate, 2.0 weight percent wool grease and 0.5 percent diphenylamine. This base grease had a mean Hertz load of 18 kg. The effect of adding phosphite ester, a selenide,

and a phosphite ester-selenide mixture to this grease iden- The data in Table II confirm the results obtained in Table I. The extreme pressure properties of stabilized anhydrous calcium greases of predominantly saturated fatty acids are decreased by the addition of a selenide but substantially increased by the addition of amyl phosphite. The grease containing the phosphite ester-selenide combination is inferior in extreme pressure properties to the grease containing the phosphite ester alone.

EXAMPLE HI A lithium base grease was prepared having the following approximate composition: 16.7 percent lithium soap of a 3:1 mixture of hydrogenated castor oil and stearic acid, 0.2 percent excess lithium hydroxide, 1.3 percent glycerine and a 3:1 mixture of a diisooctyl adipate and a paraffin base oil having an SUS viscosity at 100 F. of 100. This lithium base grease had a mean Hertz load of 19 kg. The effect of triamyl phosphite alone and of a 3:1 mixture of triamyl phosphite and dilauryl selenide on lithium base greases was demonstrated by incorporating triamyl phosphite and the mixture of triamyl phosphite and dilauryl selenide in a similar grease mixture having a higher soap content and employing aslightly difierent dialiphatic ester lubricating base, which changes do not affect the extreme pressure properties of a grease. The triamyl phosphite-containing grease mixture comprised about 20 percent lithium soap prepared from a 3:1 mixture of hydrogenated castor oil and stearic acid, 75 percent of a 3:1 mixture of di-2-ethylhexyl sebacate and paraffin base oil having an SUS viscosity at 100 F. of about 100, 0.2 percent excess lithium hydroxide, 1.5 percent glycerine and 3 percent triamyl phosphite. This grease had a mean Hertz load of 20 kg., essentially the same value possessed by lithium base grease containing no additives. The grease containing the synergistic additive mixture of thisinvention comprised approximately 21 percent lithium soap of a 3:1 mixture of hydrogenated castor oil and stearic acid, 73 percent base oil comprising a 3:1 mixture of 2-ethylhexyl sebacate and parafiin base oil having an SUS viscosity at 100 F. of about 100, 0.2 percent excess lithium hydroxide, 1.5 percent glycerine, 0.5 percent phenylalphanaphthylarnine, 3 percent triamyl phosphite and 1 percent dilauryl selenide. This grease had a mean Hertz load of 24 kg. which is only a slight improvement over the mean Hertz load values shown by the 6 lithium base grease free of additives and the lithium base grease containing triamyl phosphite.

The slight increase in EP properties effected by the phosphite-selenide mixture in a straight lithium base grease as compared with mixed LiCa base greases as shown in the following example, proves that the synergistic action is specific to the latter type greases in mixed lithium-calcium base greases.

EXAMPLE IV There was prepared a series of mixed lithium-calcium base greases in which the lithium-calcium metal ratio was 6 parts lithium to 4 parts calcium, the soap was prepared from an acid mixture comprising 3 parts of hydrogenated castor oil and 1 part stearic acid, and the base oil mixture comprised 3 parts of di-Z-ethylhexyl sebacate and 1 part of parafiin base oil having an SUS viscosity of 100 F. of about 100. In this series of greases, each member of which also contained 0.2 percent excess lithium hydroxide and 0.5 percent of an oxidation inhibitor comprising 95 parts of diphenylamine and 5 parts salicylal amino guanidine oleate, the soap content varied from 16.0 to 17.5 weight percent, the base oil content varied between 70 and 82 per cent and the glycerine content varied with the soap content but was usually in the neighborhood of about 1 to 1.3 weight percent. These variations in soap base oil and glycerine contents have no efiect on the extreme pressure properties of the resultinggrease. In Table III, there is shown the results of adding phosphite ester and selenide separately, and of adding a mixture thereof, to a lithium-calcium base grease of the above composition. Table III also shows that phosphate-selenide combinations do not have the same effect on mean Hertz load as do phosphite-selenide mixtures.

Table III Composition Mean Hertz Load, kg.

The data in Table III show that the addition of dilauryl selenide has no efiect on the mean Hertz load of a lithium-calcium base grease whereas 3 percent triamyl phosphite has a substantial elfect thereon. The phosphite ester selenide combination, however, raises the mean Hertz load value of the resulting grease substantially above that obtained with the phosphate ester alone, despite the neutral efiect of selenide ester thereon. The data in Table III also demonstrate that phosphate esterselenide combinations do not possess a synergistic EP action for mixed lithium-calcium base greases since the tributyl phosphate-dilauryl selenide mixture gives a grease of lower mean Hertz load value than does the tributyl phosphate alone.

Military specification MILG-7l18 has been established for grease to be used in the lubrication of aircraft gear and actuator screws. This grease must be capable of satisfactory lubrication at low and high temperatures, must possess good extreme pressure properties as measured by the mean Hertz load and the gear wear test, and must, in addition, he non-corrosive to copper. The low temperature requirements, copper corrosion, mean Hertz load and gear wear test requirements are considered to be the most diflicult limits composed by the MIL-G-71l8 specification. Many materials which give a satisfactory level of performance in the mean Hertz load test caused excessive gear wear or lfailure in the copper corrosion test. The use of the synergistic EP combination of a phosphite ester and a selenide in mixed 7 lithium-calcium base grease resulted in the production of a grease which met the severe limitations of the MIL-G- 7118 specification with regard to low temperature properties, copper corrosion, mean Hertz load and gear Wear test as shown in Example V.

EXAMPLE V A mixed lithium-calcium base grease containing a synergistic EP combination of phosphite ester and selenide Was prepared and met the MIL-G-7118 specification as shown in the following table. This grease had the following composition: 18.6 Weight percent lithiumcalcium soap of a 3 to 1 mixture of hydrogenated castor oil and stearic acid in which the lithium and calcium metals were present in a 6 to 4 ratio, 0.2 percent excess lithium hydroxide, 1.4 weight percent glycerine (from the hydrogenated castor oil), 75.3 weight percent of a base oil comprising 3 parts of 2-ethylhexy1 sebacate and 1 part of parafiin base oil having an SUS viscosity at 100 of 100, 0.5 percent of an anti-oxidant comprising 95 parts diphenylamine and percent salicylal amino 'guanidine oleate, 3 Weight percent triamyl phosphite and 1.0 percent dilanryl selenide.

Table IV MIL-G-71l8 Li-Oa Specification Base Grease Dropping Point, F 325 Mi.u 332. Penetration, Worked 280-340 311. Copper Corrosion (24 Hour, 212 F., Oven) Must Pass. Pass ASIM Bomb Oxidation Test:

Drop, p.s.i.-

100 Hours.

500 Hours Water Washing, Grease Loss, Percent Evaporation, Percent (22 Hours, 210 F.) Oil Separation, Percent (30 Hours, 212 F.)

Apparent Viscosity (Poises) 65 F 15 Low Temperature Torque, 65 F" 5 Max 1. HTP Hours at 250 F 1,000 M111 2,244 Working Stability, 100,000 strokes 375 Max. 308. Gear Wear Test mg. Loss/1,000 cycle 5lb. load 2.5 Max"--- 2.2. lb. load 3.5 Max--. 3.5.

30 Min .1 47.

to be used inthe lubrication of aircraft gear and actuator screws.

Obviously, many modifications and variations of the invention as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A grease characterized by EP properties comprising an oleaginous lubricating base as the major component, a mixed lithium-calcium base comprising 10-90 parts lithium soap and 10 parts calcium soap in an amount sufiicient to thicken said lubricating base to grease consistency, said soap mixture being derived from an acidic mixture comprising a minor portion of a fatty acid-containing material and a major portion of a hydroxy fatty acid-containing material, 2 to 5 percent trialkyl phosphite in which the alkyl group contains 3 to 10 carbon atoms and 0.5 to 2.5 percent dialkyl selenide in which the alkyl group contains 8 to 18 carbon atoms, said phosphiteselenide mixture imparting EP properties to said mixed lithium-calcium base grease.

2. A grease according to claim 1 containing 3 weight percent triamyl phosphite and 1 Weight percent dilauryl selenide.

3. A grease characterized by EP properties comprising an oleaginous lubricating base as the major component, 6 to 25 Weight percent of a mixed lithium-calcium soap base containing 6 parts of lithium soap and 4 parts of calcium soap, said soap base being prepared from an acid mixture comprising 3 parts of hydrogenated castor oil and 1 part of stearic acid, 2 to 5 weight percent trialkyl phosphite in which the alkyl group contains 3 to 10 carbon atoms and 0.5 to 2.5 weight percent dialkyl selenide in which the alkyl group contains 8 to 18 carbon atoms.

4. A grease according to claim 3 containing 3 Weight percent triamyl phosphite and 1 weight percent dilauryl selenide.

5. A grease according to claim 3 in which the oleaginous lubricating base comprises 3 parts of di-Z-ethylhexyl sebacate and 1 part of a parafiin base mineral oil having an SUS viscosity at F. of 100.

References Cited in the file of this patent UNITED STATES PATENTS 2,397,956 Fraser Apr. 9, 1946 2,398,416 Denison et a1. Apr. 16, 1946 2,506,049 Waitins May 2, 1950 2,588,556 Moore et a1 Mar. 11, 1952 2,646,401 OHalloran July 21, 1953 2,648,634 Moore Aug. 11, 1953 2,685,567 Harman Aug. 3, 1954 

1. A GREASE CHARACTERIZED BY EP PROPERTIES COMPRISING AN OLEAGINOUS LUBRICATING BASE AS THE MAJOR COMPONENT, A MIXED LITHIUM-CALIUM BASE COMPRISING 10-90 PARTS LITHIUM SOAP AND 90-10 PARTS CALCIUM SOAP IN AN AMOUNT SUFFICIENT TO THICKEN SAID LUBRICATING BASE TO GREASE CONSISTENCY, SAID SOAP MIXTURE BEING DERIVED FROM ACIDIC MIXTURE COMPRISING A MINOR PORTION OF FATTY ACID-CON TAINING MATERIAL AND A MAJOR PORTION OF A HYDROXY FATTY ACID-CONTAINING MATERIAL, 2 TO 5 PERCENT TRIALKYL PHOSPHITE IN WHICH THE ALKYL GROUP CONTAINS 3 TO 10 CARBON ATOMS AND 0.5 TO 2.5 PERCENT DIALKYL SELENIDE IN WHICH THE ALKYL GROUP CONTAINS 8 TO 18 CARBON ATOMS, SAID PHOSPHITESELENIDE MIXTURE IMPARTING EP PROPERTIES TO SAID MIXED LITHIUM-CALCIUM BASE GREASE. 